Visibility estimates are displayed as (i) less than 3 miles (pale yellow), and (ii) 3 miles or greater (pale blue).

IFR and VFR conditions
are determined according to the criteria given in the table below.

Flight Category

Formulation

VFR

Visual Flight Rules

ceiling ≥1000 feet

and

visibility ≥ 3 statute miles (sm)

IFR

Instrument Flight Rules

ceiling < 1,000 feet

and/or

visibility < 3 statute miles

As explained further in help page 4 ,
CVA's ceiling and visibility fields are derived through nearest-neighbor interpolation of METAR data.
This interpolation process, in effect, ‘stretches’ limited-area METAR observations across the broader
domain between stations and accounts for terrain effects on ceiling height. The resulting fields help
to visualize the ‘likely’ conditions at range from METARs. However, the reliability of these fields degrades
as distance from a METAR site increases. Thus, users should apply cautious practical judgment in considering
the representativeness of the product as distance from a METAR site increases.

METAR Station Plots

Each regional display includes station plots showing the current ceiling and visibility observations reported at selected
METAR stations. To avoid overcrowding, the display shows only a
subset of the total number of stations available. Station plot content is shown in the figure below.

Figure 1: Placement and definition of information in the station plots appearing in regional
CVA displays.

Figure 2: Guide to coding used in the cloud cover symbol. Further information on station plot coding can be found
here .

Refer to the following links for a complete list of METAR stations and associated station plots:

Viewing CVA Through the HEMS Tool

CVA can also be viewed using the HEMS
(Helicopter Emergency Medical Service) Tool available on Experimental ADDS
(see HEMS tool). The HEMS
tool viewer is approved for use by EMS (Emergency Medical Services) personnel by OpSpec (Operational Specification) A021.